1. Field of the Invention
The invention relates to the field of laser scanners for aircraft such as helicopters and, in particular, to a laser scanner of the type having additional peripheral scanning capability such that a large spatial volume is scanned in front of the aircraft.
2. Description of Related Art
Laser infrared radar, commonly referred to as ladar, is well known. In a typical ladar device, a solid state laser generates intense infrared pulses having beam widths as small as 30 seconds of arc. Ladar is commonly utilized to measure the density of clouds, smog layers, and other atmospheric discontinuities via the scattering effects afforded thereby. Ladar is also commonly utilized to track airborne objects such as balloons, smoke puffs, rocket trails, etc., via the beam reflections therefrom.
As those skilled in the art will appreciate, the use of lidar is facilitated by various mechanisms, which effect scanning of the transmitted light beam. According to contemporary methodology, it is desirable to cause the collimated laser output of the ladar device to scan in a generally circular pattern wherein the beam itself forms a cone about an axis defined along the scanned direction. Thus, as the beam is swept, the conical scanning pattern defines a substantial spatial volume. In U.S. Pat. No. 5,471,326 “Holographic Laser Scanner And Rangefinder” by J. T. Hall, et al., discloses a scanner which not only scans in a circular pattern, but moves plus or minus 12.5 degrees in azimuth, greatly increasing the area covered.
U.S. Pat. No. 5,465,142 “Obstacle Avoidance System For Helicopters And Other Aircraft” by Krumes, et al. comprises a scanner for transmitting a generally collimated beam of radiation such that the beam rotates about an axis to form a conical scanning pattern. The scanner includes a concave parabolic reflector having a geometric axis and a focus, a rotation mechanism for effecting rotation of the concave parabolic reflector about a rotation axis thereof which is angularly offset with respect to the geometric axis of the concave parabolic reflector. An opening is formed in the concave parabolic reflector near the rotation axis thereof. A convex parabolic reflector is disposed along the rotation axis of the concave parabolic reflector and has a focus, which is approximately co-located with the focus of the concave parabolic reflector.
Directing collimated radiation through the opening formed in the concave parabolic reflector and onto the convex parabolic reflector while rotating the concave parabolic reflector about the rotation axis thereof effects transmission of a generally collimated beam of radiation such that the beam rotates about the rotation axis so as to form a conical scanning pattern.
In U.S. Pat. No. 5,903,386 “Tilted Primary Clamshell Lens Laser Scanner” by M. V. Mantravadi, et al., the scanner transmits a generally collimated beam of radiation such that the beam rotates about an axis to form a conical scanning pattern. The scanner includes a concave parabolic reflector having a geometric axis and a focus point. A motor is used to rotate the reflector about an axis of rotation that is angularly offset with respect to the geometric axis of the reflector. A convex reflector is located at the focus point of the concave reflector on the rotational axis thereof. The convex reflector has a focus point co-located with the focus point of concave reflector. Thus collimated radiation directed through a hole in the concave reflector onto the convex reflector is reflected back to the concave reflector. Therefore, as the concave reflector rotates, the collimated beam of radiation is transmitted in a conical scanning pattern. The patent to Mantrvadi, et al. is a significant improvement to the prior art in that it is simple to manufacture. However, it would be desirable to provide the device with additional peripheral scanning capability such that a large spatial volume is scanned in front of the aircraft.
Thus, it is a primary object of the invention to provide a laser type scanner for aircraft and the like.
It is another primary object of the invention to provide a laser type scanner for aircraft and the like capable of scanning a large spatial volume in front of the aircraft.